1. Field
The present disclosure relates to a lignin-containing coating composition and an ultrafine fiber including the same. More particularly, it relates to a coating composition having various properties such as antibacterial property, conductivity, biodegradability, etc., an ultrafine nanofiber including the same and a method for preparing the same.
[Description about Government-Sponsored Research and Development]
This research was supervised by the Korea Atomic Energy Research Institute and sponsored by the Research Council of Science & Technology of the Ministry of Science, ICT and Future Planning of Korea. The project name was “Development of waste wood- and plant resource-based pulping and fiber formation technology using radiation” (2N44040) (project number: 1711021929).
2. Description of the Related Art
Lignin, which is a natural polymer compound together with cellulose and hemicellulose, is an oil-soluble phenolic polymer present in the cell wall of woody plants such as conifers or broadleaf trees. Lignin fills the space in the cell wall between cellulose and hemicellulose and acts as a glue. In general, it accounts for about 15-30% of dry wood by weight and plays an important role in the survival of trees by increasing the mechanical strength of woody tissue, providing resistance to attack by microorganisms, etc. However, lignin has been considered as a waste in the meantime. Because the chemical structure of lignin changes easily during the recovery process, most of lignin is recycled as a fuel in the pulping process. Lignin is difficult to hydrolyze with an acid because of its amorphous structure. Chemically, lignin is composed of phenylpropanoid units condensed by carbon-carbon or ether bonds.
Recently, as environment-friendly and renewable resources are pursued by consumers, companies and the government, interests are increasing in lignin which is abundant but has not been utilized effectively. In addition, with increasing importance of biomass as a source of bioenergy, interests are increasing in the control of lignin content in biomass using enzymes involved in lignin biosynthesis and molecular biological techniques as well as in lignin fiber formation and lignin encapsulation.
In particular, the natural polyphenol compound lignin, which is obtained as a byproduct in the pulping process, is drawing attentions because of its antibacterial and antioxidant properties originating from its structural characteristics. Lignin destroys microorganisms by damaging the cell membrane. The contents of the destroyed cells kill bacteria by exhibiting antibacterial property. Also, organic pollutants can be removed by adsorption using the microstructure of lignin. In addition, lignin can exhibit antioxidant effect because it can stabilize free radicals by proving hydrogen atoms. Due to these excellent properties, lignin is expected to be applicable as wound dressing, cellular scaffold, etc.
Carbon nanotube is a structure wherein a graphene layer is rolled into a cylindrical shape. Due to superior physical, chemical, electrical and mechanical properties, it is drawing a lot of attentions as a 1-dimensional nanomaterial applicable to various fields. However, there are many limitations in application due to the strong cohesive property of the nanomaterial. To solve this problem, methods for noncovalent functionalization using various dispersants, polymers, DNAs, proteins, etc. are suggested. In particular, methods for stabilizing and effectively controlling the dispersibility of carbon nanotube in solvents using lignin are being studied.
Electrospinning is used to form a nanofiber web, which is flexible, ultrathin and ultralight and has micropores and, therefore, can exhibit functionalities on large surface areas in various forms. However, because lignin is not suitable for electrospinning due to low viscosity, it can be mixed with PVA to be electrospun into a nanofiber web.